The present invention relates to a transfer switch, and in particular to a transfer switch that includes an improved actuator.
A transfer switch is used to switch an electric load back and forth between a primary source, such as a utility, and a secondary source, such as a generator. Transferring power from the primary source to the secondary source is necessary when the utility experiences a blackout. The transfer switch is also used to switch the power source back to utility power when the power outage is over.
A typical transfer switch is composed of an actuator and a toggle mechanism. The actuator operates by supplying energy to the toggle mechanism to maneuver movable contacts that are within the toggle mechanism relative to stationary power input contacts. The movable contacts engage one set of stationary contacts when power is supplied from the primary source and engage another set of stationary contacts when power is supplied from the secondary source.
Actuators are activated either manually or automatically at a desired time to supply energy to the movable contacts on the toggle mechanism. Many transfer switches are able to disconnect the load from both sources for a desired period of time in order to allow residual electricity to discharge before the load is switched to an alternate power source.
FIGS. 1-4 illustrate an improved electric transfer switch 10. Transfer switch 10 includes a toggle mechanism 12 (FIG. 2). The toggle mechanism 12 includes a pair of crossbars 14, 15 (FIGS. 3 and 4) that extend through the transfer switch 10. The crossbars 14, 15 in the toggle mechanism 12 are connected to an actuator 16 of the present invention that rotates the crossbars 14, 15 about their respective longitudinal axes.
A first set of moveable contacts 20 is carried by crossbar 14 and a second set of movable contacts 25 is carried by crossbar 15. Each moveable contact 20, 25 is connected to an output contact 21 and is adapted to be intermittently connected to a respective primary input contact 22 or a secondary input contact 23 depending on which crossbar 14, 15 the movable contacts 20, 25 are mounted on. Cams 29 are mounted on the crossbars 14, 15 to maneuver the movable contacts 20, 25 into, and out of, engagement with the stationary input contacts 22, 23.
FIG. 3 shows the movable contacts 20 engaged with the primary input contacts 22 when power is being supplied from a primary power source, such as a utility. As shown in FIG. 4, when there is an interruption in the primary power supply, the cams 29 on crossbar 14 rotate to disengage the movable contacts 20 from the primary input contacts 22, and the cams 29 on crossbar 15 rotate to allow the movable contacts 25 to engage secondary input contacts 23 so that power can be supplied from a secondary power source, such as a generator.
A similar operation is performed to transfer back to the primary source from the secondary source. The cams 29 on crossbar 15 rotate to disengage the movable contacts 25 from the secondary input contacts 23 and the cams 29 on crossbar 14 rotate to allow the movable contacts 20 to engage the primary input contacts 22 so that power can once again be supplied from the primary source.
Springs 28 are disposed between each of the moveable contacts 20, 25 and another portion of the transfer switch 10. The springs 28 apply a force to each movable contact 20, 25 that directs each moveable contact 20 against a corresponding stationary input contact 22, 23.
During the operation of a typical transfer switch there may be extreme conditions where the movable contacts can become slightly tack welded to the stationary contacts. Known actuators are often unable to apply a large enough force to the contact-carrying members within the transfer switch to permit the contacts to open in a desired amount of time. In addition, existing actuators often times do not allow for different programmed transitions of the movable contacts within the transfer switch between the stationary input contacts of the alternative power sources. One example of a programmed transition could be where one set of moving contacts is disengaged from the primary input contacts followed by a predetermined delay before the another set of movable contacts is engaged with the secondary input contacts.
There is a need for actuator 16 which can be used with transfer switches that include two rotating crossbars. Actuator 16 is able to independently operate the two crossbars and generate enough operating force to separate any tack-welded contacts that need to be maneuvered by the crossbars. Actuator 16 is also be able to provide for a variety of programmed transitions between two separate power sources.
The present invention relates to a transfer switch that includes an actuator which is capable of independently operating two rotating crossbars within the transfer switch. Since the crossbars in the transfer switch are operated independently, the actuator may include two similar but interrelated mechanisms such that one mechanism maneuvers one crossbar and the other mechanism maneuvers the other crossbar.
Using two mechanisms within a single actuator facilitates operating the actuator with a variety of programmed transitions between two separate power sources. One such transition could involve including a predetermined delay before switching power sources. Another programmed transition could be a closed transition where both sets of movable contacts within the transfer switch are simultaneously engaged with the primary and secondary input contacts before one set of movable contacts is disengaged. The closed transition provides a no break transfer of power from one source to another. No break power transfers are likely to increase the service life of the contacts within the transfer switch, as well as providing the primary function of supplying loads that can not tolerate any kind of interruption, however brief.
In addition, it is easier to design each of the mechanisms so that they generate a larger operating force on the crossbars than could be generated by a single mechanism. The larger operating force on each crossbar helps separate the movable contacts when the contacts have become tack-welded together.
The transfer switch includes output contacts, primary input contacts, secondary input contacts and a toggle mechanism. The toggle mechanism includes moving contacts that alternately connect the output contacts with the primary and secondary input contacts. The transfer switch further includes an actuator that rotates the first crossbar to alternately engage a first set of moving contacts with the output contacts and the primary input contacts, and rotates the second crossbar to alternately engage a second set of moving contacts with the output contacts and the secondary input contacts.
The present invention also relates to a method of actuating a transfer switch to alternate the supply of power to an electric load. The method includes rotating a first crossbar within the transfer switch to engage a first set of switching contacts with a primary power source. The method further includes rotating a second crossbar within the transfer switch to engage a second set of switching contacts with a secondary power source.
The present invention also relates to a transfer switch that includes output contacts, primary input contacts, secondary input contacts and a toggle mechanism which has a first crossbar and a second crossbar. The transfer switch further includes means for rotating the first crossbar to engage a first set of switching contacts with a primary power source and rotating the second crossbar to engage a second set of switching contacts with a secondary power source.
In another aspect, the present invention is directed to an actuator for a transfer switch. The actuator includes a pair of couplings that are each adapted to be connected to a separate crossbar in the transfer switch, and a pair of indexing mechanisms that are each engaged with a separate one of the couplings to apply torque to the couplings. The actuator further includes a pair of crankshafts that are each engaged with a separate one of the indexing mechanisms to apply torque to the indexing mechanisms, and a pair of stored energy devices that are each engaged with a separate one of crankshafts to apply torque to the crankshafts using energy released by the stored energy devices.